On Thursday, two environmental groups pointed to 25 jewels of the National Park System as examples of how climate change poses an immediate threat to America’s recreational, historical, and scenic gems.

Already, glaciers are expected to disappear from Glacier National Park within 15 years. Saguaro National Park may lose its saguaro cactuses. Grizzly bears may lose one of their most important food sources. The list of dangers prompted by climate change goes on and on.

The parks are experiencing a rare moment in the national spotlight, largely thanks to the television series “National Parks: America’s Best Idea” now airing on PBS, the work of award-winning documentary filmmaker Ken Burns. The report’s sponsors said in a telephone press conference that they had not intentionally planned for their report to be issued at the same time as the PBS series was being broadcast.

“The Park Service has to decide if it’s serious about this,” said Stephen Saunders, president of the Rocky Mountain Climate Organization and the report’s principal author.

“What we choose to do will make an enormous difference as we go forward,” Mr. Saunders said. He urged Americans to “put pressure on legislators” to address this issue.

The NPS is also suffering from a $9 billion to $11 billion backlog in needed maintenance on park infrastructure, such as roads, trails, bridges, and dams. That’s on top of an annual $800 million deficit for the routine operation of the parks.

Among the risks to US national parks outlined in the report are:
– A loss of ice and snow.
– A loss of water.
– Higher sea levels and stronger coastal storms.
– Downpours and flooding.
– Loss of plant life.
– Loss of wildlife.
– Loss of fish.– Loss of historical and cultural treasures.

Among the report’s 32 recommendations:
– The US government must sign on to reduce greenhouse gases emissions by 20 percent by 2020 and by 80 percent by 2050.
– Congress should expand current national parks and create new ones.
– The NPS should create specific plans for how each park will address climate change.
– Parks should become “climate neutral” in regard to their own human-created greenhouse-gas emissions.
– Parks should educate visitors about the threat of climate change to the parks.
– Parks should be freed to use their entrance fees toward addressing climate change issues in the park.– Parks should be allowed to conduct scientific research within their borders, a function that was transferred by Congress to the US Geological Survey in 1993.

The National Park System includes 391 parks and other properties managed by the NPS. The list of 25 national parks most in danger includes some of the most visited and well-known parks from coast to coast, including Yellowstone, Yosemite, and Zion in the West; Ellis Island in New York harbor and Acadia on Maine’s rocky seashore.